1. Field of the Invention
The present invention relates to a system having a process chamber such as the heat process and load lock chambers of the vertical type and serving to support and rotate substrates such as semiconductor wafers, which are to be processed, in the process chamber. The present invention also relates to a method of supporting and rotating the substrates in the process chamber.
2. Description of the Related Art
When the heat-diffusing, heat-oxidizing or CVD film forming process is to be applied to the semiconductor wafers, the heat process apparatus of the vertical type is usually used. In the case of the heat process apparatus of the vertical type, a wafer boat is rotated round a vertical shaft in a process tube so as to enable a certain processing rate to be achieved. A boat supporting and rotating system has a double-magnet structure in which an outer (or drive) magnet and an inner (or driven) magnet are combined with each other to seal the process chamber from outside. When the outer magnet is rotated in this case, the inner one is also rotated following the outer magnet. In short, the boat supporting and rotating system is intended to use the magnetic interaction of the outer and inner magnets to transmit rotation force to the wafer boat. The wafer boat is rotated together with the inner magnet in this case.
Rare earth magnets are used as these inner and outer ones. They have a strong coercive force and an excellent heat resistance, but they are fragile and easily broken. They are therefore nickel-plated to prevent particles from being caused from them. When impact is added to them, however, the layer of nickel-plate is peeled off from them and metal contamination is caused accordingly. When magnetic material is thus exposed, it is eroded by erosive process gas and the amount of particles thus caused is increased accordingly.
In order to prevent oil contamination, the boat supporting and rotating system uses ceramics bearings which make it unnecessary to use lubricating oil in the bearing casing. However, each of these ceramics bearings is a combination of materials of different kinds. Particles are thus easily caused. When the process tube is exhausted after the wafer boat is carried into it, particles in the bearing casing of the boat supporting and rotating system are scattered into the process tube to thereby contaminate the wafers. In the case of the conventional boat supporting and rotating system, therefore, particles scattered into the process chamber cause metal contamination. This causes the productivity of the apparatus to become low.